VulnerabilityPublished 1 Apr 2026

CVE-2025-66442: mbedtls · Covert Timing Channel

Affects mbedtlsSource CVE Database V5

Not known to be exploited · CVSS 5.1 Medium.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

5.1Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 19% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack Vector: Local
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 1 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
GitHubmbed-tls/mbedtls`pkg:github/mbed-tls/mbedtls`Other threats	Affected <=4.0.0	Fixed in–
GitHubmbed-tls/TF-PSA-Crypto`pkg:github/mbed-tls/TF-PSA-Crypto`Other threats	Affected <=1.0.0	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2025-66442, organizations should first identify whether their cryptographic libraries are compiled with LLVM's select-optimize feature enabled. If so, recompiling Mbed TLS and TF-PSA-Crypto without this optimization or using alternative compiler settings that avoid the timing side channel is recommended. Developers should apply any patches or updates released by the Mbed TLS and TF-PSA-Crypto maintainers once available. Employing constant-time cryptographic coding practices that are resilient to compiler optimizations is essential to prevent similar issues. Additionally, performing side channel analysis and testing on cryptographic builds can help detect timing leaks introduced by compiler behavior. For critical systems, consider using hardware-based cryptographic modules that are less susceptible to software timing attacks. Monitoring cryptographic operations for anomalous timing patterns and restricting access to cryptographic keys can further reduce risk. Finally, maintain awareness of compiler updates and security advisories related to cryptographic libraries and build environments.

Description

In Mbed TLS through 4.0.0, there is a compiler-induced timing side channel (in RSA and CBC/ECB decryption) that only occurs with LLVM's select-optimize feature. TF-PSA-Crypto through 1.0.0 is also affected.

Impact

The primary impact of CVE-2025-66442 is the potential compromise of cryptographic key confidentiality through timing side channel attacks. Organizations using affected versions of Mbed TLS or TF-PSA-Crypto in embedded systems, IoT devices, or security-sensitive applications could face unauthorized disclosure of private keys or plaintext data. This could lead to broader security breaches, including interception of encrypted communications, unauthorized access to protected systems, and undermining of trust in cryptographic protections. The vulnerability's dependence on a specific compiler optimization means that some builds may be vulnerable while others are not, complicating risk assessment. The absence of known exploits reduces immediate risk, but the subtlety and difficulty in detecting the flaw increase the long-term threat. Industries relying heavily on embedded cryptography, such as telecommunications, automotive, industrial control, and consumer IoT, may experience significant exposure. The impact on integrity and availability is minimal, but the confidentiality breach potential is significant, especially in environments where cryptographic keys are critical assets.

CWE-385Covert Timing Channel (opens in a new tab)
Base weaknessLikelihood of exploit: Medium
Covert timing channels convey information by modulating some aspect of system behavior over time, so that the program receiving the information can observe system behavior and infer protected information.
Architecture and Design
Whenever possible, specify implementation strategies that do not introduce time variances in operations.
Implementation
Often one can artificially manipulate the time which operations take or -- when operations occur -- can remove information from the attacker.
Implementation
It is reasonable to add artificial or random delays so that the amount of CPU time consumed is independent of the action being taken by the application.
OWASP Cheat Sheets
Cryptographic Storage (opens in a new tab)
Key Management (opens in a new tab)
OWASP ASVS 4.0.3
V6.2.8 (opens in a new tab)
Attack patterns
Cross-Domain Search Timing (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 1 Apr 2026, 20:08 UTC

WeaknessesCWE-385

Technical details

References

Community reviews

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